The Compatibility button will invoke the Upgrade API Analyzer tool: In case you select Do not update option, nor the existing resources will be updated, neither the new ones will be added.

If the Update where already in use option is checked, the existing resources will be updated but no new files will be added.

NET AJAX Control Toolkit that delivers some improvements as well as a few user-requested updates to a number of the controls in the suite. NET Ajax Control Toolkit (or, simply, Ajax Toolkit) sports some improvements in a number of controls, such as a client-side selected Index Changed event for Combo Boxes, copy/paste capability from MSWord to the HTMLEditor Extender control that retains formatting; and an On Click event added to the Rating control.

Two other requested features that made it into this release are an updated tutorial for adding custom controls, and a tutorial as well as the ability to create custom localizations.

(Good job, I would up vote your answer but no reputation).

Ajax Control Tookkit should show under References for the project.

It also gives you the ability to choose whether to create a backup of the project or not: After choosing the preferred options and pressing the Finish button, the Upgrade Wizard will replace the existing assemblies in the selected project(s) with the ones from the selected distribution.

The wizard will update only assemblies that are currently referenced, e.g.

These features are available in all controls to which they apply.

A number of bugs that pervaded many of the controls have since been fixed, and are listed in this blog post from Dev Express Program Manager Mehul Harry.